1. Field of the Invention
This invention relates in general to an in vivo mechanical energy source. More particularly, it relates to a miniaturized mechanical motor that is small enough to fit inside a percutaneous transluminal device and yet powerful enough to do work.
2. General Description of the Art
Catheters are used in a variety of percutaneous transluminal treatments, such as coronary, cerebral and peripheral angioplasties. The general objective of these treatments is to open obstructions or lesions within a body vessel such as a blood vessel. For example, in percutaneous transluminal coronary angioplasty (PTCA), a guide catheter is introduced at an appropriate location in the patient's body and routed through the vascular system into the aorta and coronary orifice. A thin and relatively flexible guide wire is advanced through the guide catheter to the arteries, and then steered into side branches (if necessary) to access the obstruction. Once the guide wire has established a path across the obstruction, an "over-the-wire" dilatation balloon catheter is passed over the proximal end of the guide wire until the balloon is adjacent the obstruction. The balloon is then inflated by introducing a fluid into the balloon through an inflation lumen in the catheter. The inflated balloon expands against the blockage to dilate the obstructed blood vessel. Another type of balloon catheter known as "fixed-wire," eliminates the need for a separate guide wire by attaching a short flexible guide wire to the distal end of the catheter.
Other methods of treating blocked blood vessels involve the use of miniaturized mechanical devices to cut, abrade, or otherwise open a passage through the obstruction. For example, U.S. Pat. No. 4,936,845 discloses a catheter having a rotating head at its distal end for boring a passageway through an obstructed blood vessel. U.S. Pat. No. 4,854,325 discloses a guide wire that is mechanically driven through a ramming back-and-forth action to assist in forming a pilot passageway through the obstruction. Other miniaturized mechanical devices are disclosed in U.S. Pat. Nos. 5,007,917; 5,011,490; 5,030,201; and 5,059,203.
The mechanical devices disclosed in the above-identified patents are driven by external motors which are connected to the device through a drive shaft extending along the length of the catheter. There are several problems with transmitting mechanical energy down a relatively long drive shaft in a catheter. For example, the drive shaft dissipates a significant amount of the mechanical energy into the patient's blood vessel. This can cause considerable trauma, and the patient often requires drug treatments to counteract the negative effects. The dissipated mechanical energy also results in large energy losses. Because of the small dimensions of the vascular system, the energy needed at the in vivo work site is typically less than 1 watt. However, due to the tremendous energy losses through the drive shaft, external motors must typically generate about 100 watts in order to produce less than 1 watt at the in vivo work site.
Also, external motors are large and can require complicated connectors for coupling them to the relatively small drive shaft. In addition, drive shafts are relatively rigid, and accordingly, they are difficult to negotiate through the vascular system. Thus, the placement of a drive shaft along the length of a catheter severely compromises the catheter's flexibility.
U.S. Pat. No. 5,176,141 issued to Bom discloses a disposable ultrasonic catheter that has a rotatable acoustic mirror for directing sound waves outwardly into tissue and for receiving echo sounds and directing the echo sounds to a transducer. The transducer's output is transmitted to a visual display which displays an ultrasound picture of the tissue whereby one can determine the makeup of the tissue, e.g., hard or soft. A motor is provided in the catheter for rotating the mirror at selected rpm.
The mirror in Bom is a very tiny and light weight acoustic crystal transducer. The motor that rotates the mirror is illustrated only as a cylinder 3 in FIGS. 1-3 of Bom. Bom provides no details about the construction and operation of its motor, except to describe it as a "multi-polar microsynchronized motor." Bom, col. 4, lines 11-12. Accordingly, the motor disclosed in Bom is not capable of delivering the more than about 0.01 watts of energy that would be needed in order to do any appreciable work such as pumping blood (preferably via a perfusion pump) or operating dottering devices, inflation pumps, atherectomy devices, and other such devices.
Thus, it would be beneficial to provide a mechanical energy source that is powerful enough to do work yet small enough to fit inside a body vessel, thereby allowing the mechanical energy source to be placed inside a percutaneous transluminal device and in close proximity to a load at the distal end of the device.
Thus, it would also be beneficial to provide an in vivo perfusion pump that is specially adapted to be used with an in vivo mechanical energy source, said energy source being powerful enough to do work yet small enough to fit inside a body vessel.
The following terms are used throughout this disclosure and are intended to have the following meanings:
The term "distal" refers to the end of the percutaneous device that is inserted in the patient's vascular system.
The term "proximal" refers to the end of the percutaneous device that is outside the patient's vascular system.